L7 - Cell mediated allergy

What Coombs and Gell hypersensitivity Class does cell mediated allergy fall under?

Class IV hypersensitivity

What is a major disease that occurs in cell-mediated allergy?

Allergic contact dermatitis

What are some common ways to develop allergic contact dermatitis?

Dermatological visits, industrial illness, Rhus dermatitis, etc.

Evaluating allergic contact dermatitis through dermal manifestations is easier than systemic manifestations. How is this done?

Via delayed hypersensitivity tests

Describe a delayed hypersensitivity test

A small amount of an antigen is injected into the skin. If the person has been previously exposed to the antigen, memory T cells will trigger an immune reaction, leading to redness, swelling, and induration at the injection site within 24-72 hours.

Cell-mediated allergies can also present as allergies of ______ disease

infectious

What is another term for cell-mediated allergies or Class IV hypersensitvity?

Delayed-type hypersensitivity (DTH)

Class IV hypersensitivity reactions are mediated by what cells?

Antigen-specific effector T cells

What are some common antigens of delayed-type hypersensitivity?

Insect venom, mycobacterial proteins, etc.

(poison ivy, DNFB, nickel, chromate, etc.)

What are some common reactions seen in DTH?

Local skin swelling such as erythema, induration, cellular infiltrate, and dermatitis

What are some common antigens of contact hypersensitivity?

Haptens such as pentadecacatechol (poison ivy) and DNFB. Small metal ions such as nickel and chromate

What are some common reactions seen in contact hypersensitivity?

Local epidermal reactions such as erythema, cellular infiltrate, vesicles, and intraepidermal abscesses

Are antibodies involved in cell-mediated allergy?

No

What is the clinical significance of cell-mediated allergy?

It can cause allograft rejection, graft-vs-host disease, pathology of virus diseases, autoimmune disease, and adverse drug reactions

Reminder: How does graft vs host disease work?

Some cell transplants contain mature and memory T cells from the donor. These will travel to secondary lymph tissues and proliferate. They then will begin to attack recipient cells because they are foreign

Contrast graft vs host disease with organ rejection.

Graft-vs-Host Disease: The donor’s immune cells attack the recipient’s tissues, recognizing them as foreign.

Organ Rejection: The recipient’s immune system attacks the donor organ, recognizing its antigens as foreign.

Describe the allergens that cause allergic contact dermatitis

Small, lipid soluble molecules that can pass the stratum corneum

What is extrinsic allergic alveolitis?

Also known as hypersensitivity pneumonitis (HP), which is an inflammatory condition of the lungs

Describe the allergens that cause extrinsic allergic alveolitis

Organic dusts typically from occupational source

What other hypersensitivity class is involved in extrinsic allergic alveolitis?

Class III hypersensitivity

Why is Class IV hypersensitivity more damaging in regards to extrinsic allergic alveolitis compared to Class III?

Class III hypersensitivity involves forming specific immune complexes with IgG and it can be difficult to achieve the correct size to activate complement. Class IV can activate easier

Give the first step in the production of a cell-mediated allergy

An individual is exposed to an allergen or a substance that can trigger the immune response. This could be poison ivy (urushiol), nickel, etc.

Give the second step in the production of a cell-mediated allergy

Dendritic cells capture the allergen and then process the antigen and present it to naive T cells in the lymph nodes.

Give the third step in the production of a cell-mediated allergy

Once activated, T helper cells become sensitized to the antigen, and they differentiate into TH1 cells

Give the fourth step in the production of a cell-mediated allergy

Some of the activated T cells become memory T cells, which remain in the body for future encounters with the same antigen.

Give the fifth step in the production of a cell-mediated allergy

Re-exposure to the antigen activates memory T cells (TH1) that release cytokines such as IFN-gamma, TNF-α, and interleukins.

What do the cytokines do in cell-mediated allergy?

Activates macrophages and increases inflammatory mediators which leads to tissue damage

IgE (type I) reactions tend to involve TH____ while cell-mediated (type IV) tend to involved TH____

2; 1

1 multiple choice option